The present invention relates to a method and device for assessing the clogging risks of a well or bore hole passing through a porous reservoir, more particularly a geological formation fed by a water bearing nappe and for determining in advance the characteristics to be given to production works, wells or bore holes, for avoiding clogging thereof.
These characteristics will for example be the diameter of the main well and its liner, the lined height, the position and characteristics of the radiating drains, the pumping rate and the lowering height of the ground water.
A first application of the invention resides in a diagnosis of the life span of worked bore holes and wells and of the working methods and procedures likely to extend it.
A second application of the invention resides in the proposal of curative or corrective treatment for a reservoir or work which risks being clogged.
Clogging phenomena affect numerous wells or bore holes passing through geological formations, particularly granular geological formations.
These phenomena reduce the working life of these works sometimes to a few years; whereas their financial amortizement is generally calculated for a twenty year period.
The financial repercussion of clogging is so great that efforts have been made for numerous years to discover means for reducing the amount of clogging when it affects the works. This search for curative means has not yet had notable success for it is often too late to act efficiently. This is why it is desirable to be capable of foreseeing beforehand the risks of clogging of a reservoir by an overall knowledge of its properties and of the evolution thereof as a function of the fluid flow in the reservoir, for example a water bearing nappe. The properties, the overall knowledge of which is important, are not limited to the properties alone of the fluid which occupies the reservoir. The clogging index is known from the fouling of a cellulose acetate membrane with a porosity of 0.45 after 15 minutes of filtration by water taken from an aquifer. Now this index does not take into account the geological formation which experimentation has not been able to reveal. The absence of the porous medium in this determination means that the physiochemistry of the interfacial phenomena cannot be correctly simulated, just as the development of microorganisms in the pores and small channels of the medium cannot be reproduced.
By way of prevention, it is advisable to determine the flow speed of the fluid during pumping or injection, which should not be exceeded so as to avoid clogging. The method of the invention allows this determination to be made on the site itself by feeding a physical model formed of several test specimens through which the fluid is caused to percolate at different speeds.